1. Field of the Invention
The present invention relates to a twin disk type tool turret mechanism for a NC machine, more particularly one, which is equipped with single stepper motor or a servomotor, instead of conventional hydraulic mechanism, as the power source for internal and external tool turrets thereof such that the turret mechanism can be improved in respect of efficiency and reliability, and can be used with a precision control for increasing the efficiency in tool choosing action, and can be made simpler in the structure.
2. Brief Description of the Prior Art
In U.S. Pat. No. 4,706,351, a twin disk type tool turret mechanism is taught, which includes:
a turret housing;
front turret and a rear turret means mounted in the housing, the two turrets being mounted so that they can be separately rotated for tool selection with said rear turret being axially fixed and said front turret being axially moveable;
three-piece toothed coupling means having first, second and third coupling elements connected respectively to the front turret, rear turret and turret housing means for interlocking the front and rear turrets against rotation, the coupling elements being constructed so as to be unlocked upon axial movement of the front turret away from the rear turret by disengagement of the teeth of one of the first or second coupling elements from the teeth of the third coupling element and the other of the first or second coupling elements to release said turrets for rotation;
several OD turning tools and a first workpiece measuring probe radially disposed on the front turret for outside cutting and measuring operations;
annular body means on the rear turret adapted to receive several devices from the group consisting of boring tools, a second workpiece measuring probe, rotary tools for milling and drilling, end lathe tools and OD turning tools, which are axially disposed on a periphery of the annular body means;
transmission means including a hydraulic cylinder device and a gearing system installed in said turret housing means and mechanically connected to both turrets for separately operating the turrets;
a hydraulic system provided in the turret housing and functionally coupled with the transmission means and the turrets for respectively controlling the rotation of the turrets;
inter-disc contact means and inductive signal transmission means respectively installed in the front and rear turrets for automatically measuring outside and inside diameters of a workpiece in process; and
a cutting fluid supply system, including a passageway extending along the central axis of the turret housing means, for supplying cutting fluid to any tool in an active position during the operation of either turret.
Thus, both turrets can be separately operated without interference and tools can be operationally disposed in the turrets without increasing the turret size.
Although the tool turret mechanism can help increase efficiency and speed of NC lathes, it is found to have disadvantages as followings:    1. Because single hydraulic motor is used as the power source, for which the hydraulic oil passages are relatively complicated in structure, maintenance cost of the whole machine will increase. And, switching mechanisms, and control, which are used together with the hydraulic motor, are also expensive, and cost much to maintain.    2. Because conventional hydraulic motors have relatively long reaction time in switching and controlling, the power source, i.e. the hydraulic motor, isn't efficient, not suitable for use with high speed machining centers.    3. Because the front and the rear turrets are actuated with the hydraulic power, there have to be two sets of rotary switches respectively provided for the front and the rear turrets. Consequently, there will be too many joints, increasing the cost and failure rate.    4. Cutting fluid is supplied to the front tool turret, and the rear tool turret in sequence through the central shaft therefore fluid passages have complicated structure, and cost much to build. Furthermore, the cutting fluid guiding mechanism has to be made such that water supply can stop when the front tool turret is in a certain one of the various positions; thus, water supply can be first made to stop before each switching action. Otherwise, water will be ejected, and efficiency of tool choosing action will be reduced. Therefore, the cutting fluid guiding mechanism is not convenient.    5. The front and the rear tool turrets are separately actuated, and have small spaces in between. Consequently, cuttings and dirt will be deposited in the small spaces between the front and the rear turrets to cause the precision of the turrets to reduce.    6. There has to be more space provided for containing the complicated cutting fluid passages as well as for allowing switching of the cutting fluid guiding mechanism therefore the length of the shanks of tools, and the distance between outer ends of the front and the rear turrets have to be increased. Consequently, dimension, weight, and cost of the whole machine will increase, and the turret mechanism isn't suitable for high speed machining, and the precision of machining can't be maintained, and the surface of work pieces will be rougher, and service life of the tools can be shortened.